In the Finnish Patent number 98810 there has been presented a water purification device, that is partly of the type above and that has a Membrane-structured filtering film. The solution in question is meant to operate on so called syphon principle, thanks to which the structure of the same is very simple. The water purification device in question is very safe and easy to use in practice, because the quality of the water flowing down to the collecting point, taking place thanks to the syphon phenomenon self-powered and continuously, is always homogeneous regardless of the user of the device. This is first of all due to the fact, that a water purification device equipped with a thin PTM- or TeM filtering film does not at any stage let through material parts exceeding a certain particle size, in which case, when the filtering film gets dirty, only the penetration speed of the filter decreases and may even totally be interrupted, in case the filtering film is not cleaned every now and then.
The type of device described above is very easy to use in most heterogeneous connections, e.g. for filtering of lake water on terrain or under other circumstances as well, when so called tap water may not be exploited or when it is not drinkable. A disadvantage of the device in question is mainly the fact; that e.g. in ordinary household use, the device requires use of separate vessels, so that the syphon phenomenon may be carried out.
On the other hand, nowadays there are water purifying devices on the market also, which have a so called primary space and a secondary space built-in with the same body. One purifying device existing on the market nowadays has name “KATADYN, Type TRK”, that is based on ceramic filter cartridges, that exist in a uniform reservoir and that let through water gravity-operated from a primary space to a secondary space, that is placed underneath the primary space and that is equipped with a tap in order to run filtered water. In the solution in question there has been exploited furthermore activated carbon, that is placed inside the ceramic filter.
Functioning of this type of structure is inadequate first of all thanks to its slowness (about 40 litres/24 hours), which is among other things due to the fact, that when the level of water surface gets down, the filtering surface of the filter gets continuously smaller. Ceramic material has furthermore such a disadvantage, that ceramic filtering material absorbes substances existing in the water to be treated, such as humus or like, which is why it first of all gets dyed thoroughly and on the other hand naturally lets a large quantity of fine-grained humus through the same. This is why a ceramic filter clogs up in the course of time and it is not possible to “open” the same or in other words e.g. wipe it clean otherwise than peeling off its surface, thanks to which the substance layer carrying out filtration gets thinner, which finally causes a risk for reliability. When using this type of solution, one may not under all circumstances have full certainty, whether the water, that has been treated is totally safe for drinking, that is why it is safest to avoid use of the type of purifying device described above under particularly disadvantageous circumstances.
On the other hand, there are on the market nowadays also water purifying devices being sold under name “BRITA” or “AQUALETTE, LEIFHEIT”, that are based on lighter structures in such respect, that merely activated carbon for water filtration and purifying has been exploited therewith. This is why it is not technically taken possible to reach the level of ceramic filters described above, that is why this type of solutions are applicable mostly for tidy housekeeping purposes, wherein the meaning is mostly to remove e.g. taste of chlorine from water. Actual removal of bacteria is not enabled by the type of solutions.